Pumps and compressors



June l, 1965 c. R. SCHNEIDER PUMPS AND GOMPRESSORS Filed March 25, 1963-vam-f |NvENroR= ZZM United States Patent 3,186,343 PUMPS AND COMPRESSORSCharles R. Schneider, Wesleyville, Pa. (U.S.S. Wm. R. Rush (DD-714),Fleet Post Olce, New York, N.Y.) Filed Mar. 25, 1963, Ser. No. 267,453 1Claim. (Cl. 103--38) This invention relates to reciprocating piston orplunger machines, ordinarily called reciprocating compressors or pumpsand particularly to means for varying the discharge of said machineswhile maintaining constant pressure. In the following these machines arecalled pumps although I desire it to be understood that everything notedhereafter will apply to compressors too.

In the conventional reciprocating pump the stroke of the pump isconsidered constant and thus the discharge of the pump is constant also.This condition is not always desirable as in the case when the dischargeline of the pump is closed. In this instance the conventional pump woulddevelop an excessive high discharge pressure while attempting todischarge a constant amount of fluid. As a consequence of theconventional pump operation, the discharge pressure of the pump isdependent on the rate of discharge from the pump. Thus a constant strokeand displacement pump has a constant discharge but a continuouslyvarying discharge pressure. In some pump designs an external reliefvalve opens at the maximum permissible pressure to bypass the excessivefluid which is returned to the inlet of the pump whenever the systemserved by the pump does not require additional lluid. The powerconsumption at such a condition is high, vbecause the pump displaces aconstant amount of bypassed fluid against the maximum pressure. In orderto avoid this waste of power an external shut-off switch is usuallyattached to the relief Valve in these designs which interrupts theelectric current to the motor and stops the operation of the pump.Whenever the system requires additional iluid the discharge pressuredecreases, the relief valve closes, the switch connects the electriccurrent -to the motor and the pump operates again. In order to actuatethe switch the relief valve must move through a considerable distancewhich in turn causes a disagreeable large drop of the maximum pressurein the system served by the pump. For large motor-pump aggregatesfrequent starting is undesirable or outright impossible. In order toavoid the high power consumption at idling or the numerous start andstop operations of the motor in lsome reciprocating pumps means havebeen incorporated to vary the length of the stroke of the piston. Thesemeans involve a great deal of linkage apparatus and usually a sensorelement from the discharge line to the pump.

It is, therefore, desirable to provide an arrangement for varying thelength of the stroke of the piston which eliminates the mechanical andhydraulical linkages including sensor elements of the present designswith their inherent slow response and inertia effects and whicheliminates also the necessity of external relief valves and shut-offswitches.

An object of this invention is, therefore, a pump which maintains aconstant discharge pressure regardless of the variations in ilow byincorporating a simple, highly sensitive and rapidly responding device.

Further objects and advantages of this invention will become apparentand the invention will be better understood by reference to thefollowing description and the accompanying drawing, and the features ofnovelty which characterize this invention will be pointed out withparticularity in the claim annexed to and forming a part of thespecification.

In accordance with the broadest aspects of this invention, a piston of apump is fastened to the piston ice rod by means of a spring which willallow a relative motion between the piston and the piston rod due to thecompressibility of the spring.

In the drawing:

FIG. 1 is a side elevational view, partly in section, illustrating theimproved construction of a conventional pump.

FIG. 2 is also a side elevational View partly in section, furtherillustrating the improved construction of a conventional pump showing adifferent position of some of its parts.

Referring now to the drawing, there is shown a cyl` inder 1 having apiston rod 2 and a spring mounted piston 3 within. A discharge valve 7and an intake valve 8 are included to complete the operationalcharacteristics .of the pump The piston 3 and the piston rod 2 are soassembled that the piston can move relative to the piston rod in anaxial direction. The piston stop 4 is fastened securely to the pistonrod 2 by offsetting, welding or by threads such that the piston rod 2does not project past the lower side of the piston stop 4. The piston 3itself may be of any configuration, with reference to sealing rings,seals, gaskets and so forth between the piston 3 and the cylinder 1 andbetween the piston 3 and the piston rod 2 as long as said piston 3 canmove relative to the piston rod 2 in an axial direction. In thisparticular drawing the seals between the sliding surfaces of the piston3 against the inner wall of the cylinder 1 and of the piston 3 againstthe piston rod 2 are obtained by keeping the clearances between saidsurfaces Very small.

The piston 3 is also provided with a counterbore at its lower end whichpermits the retraction of the piston stop 4 into the piston 3 so thatthe lower surfaces of said piston 3 and said piston stop 4 are ush asshown in FIG. 2. The actuating spring 5 is essential to the pumpsoperation. The size and characteristic of said spring 5 would beselected by the operating conditions for which the pump is intended. Theinner diameter of the spring 5 must be larger than the diameter of thepiston rod 2. Furthermore, the bottom face of the spring 5 must restagainst the top face of the piston 3 and the top face of the springagainst an axially adjustable plate, the output selector 6. The innersurface of the output selector 6 is threaded and will mate with thethreads of the threaded portion 9 of the piston rod. After adjusting theoutput selector 6 on the piston rod 2 to the desired spring force byrotating it around the thread 9 the said output selector 6 will belocked in place by any convenient means like lock-nuts, set Screws orsimilar devices. In this drawing a self-locking friction thread 9 isused for this purpose. Like in conventional pumps the space above thepiston 3 in the cylinder 1 is provided with a suitable drainhole (notshown) to permit any fluid which leaks from the lower part of thecylinder 1 past the piston 3 into the upper part of the cylinder 1 toescape to the outside.

It will be readily seen that the fluid pressure below the piston 3forces said piston 3 against the spring 5. As long as the initial springforce as adjusted and maintained by the output selector 6 is larger thanthe force exerted by the tluid pressure against the lower face of thepiston 3, the said piston 3 and the piston rod 2 with its piston stop 4operate as a single unit like in any conventional pump. This conditionis illustrated in FIG. 2. In FIG. 2 the piston 3 together with thespring 5, the output selector 6, the piston rod 2 and piston stop 4 movedownward as a single unit. The fluid is forced out under pressurethrough the discharge valve 7. The intake Valve 8 is closed by the samepressure as in any conventional pump. After attaining the full stroketravel distance of the piston rod 2 the said single unit reverses itsmotion and moves upward (not shown). In this case the discharge valve 7would be closed and the intake valve 8 would be opened by the enteringnew fluid as in any conventional pump.

However, if at a subsequent downward stroke the force exerted by theincreasing pressure of the fluid against the lower surface of the piston3 equals the preadjusted force of the spring against the upper surfaceofthe piston 3 the motion of the piston 3 will be stopped. Thismomentary condition is shown in FIG. 2. However, the piston rod 2 rnustcomplete its stroke. It travels with the piston stop 4 and the outputselector 6 farther downward. This position is shown in FIG. 1. Thepiston 3 in FIG. 1 remains at the same height as shown in FIG. 2 whilethe piston stop 4l with the piston rod 2 moved lower into the iiuid.Since the output selector 6 moves also lower the spring 5 in FEG. 1 iscompressed. This will increase the pressure of the fluid slightly. Thisvariation of maximum pressure can be held to a permissible minimum bydesigning properly the length of the spring between the pistonV 3 andthel output selector 6 in the preadjusted position as shown in FIG. 2.The ratio between this lengt and the subsequent deflection due tocompression as shown in FG. 1 must be equal to the ratio between themaximum pressure and the permissible maximum pressure variation.

It will be readily seen that the piston 3 does not move anymore when thesystem served by the pump does not require additional iuid. In this casethe pump can operate at full speed without transporting any fluid. Thepower used by the pump can be calculated by obtaining the product of therate of volume of the uid passed by the pump times Vthe fluid pressure.Since the piston 3 is motionless and the volume passed is zero, thetheoretical power consumption is zero also. Therefore, the said pump canidle at full pressure with idling power losses only, which consistmainly of friction losses. The frequent start and stop of pump motors iseliminated.

While a spring 5, an adjustable plate, called output selector 6 and acounterbore in the piston 3 :tor the retraction of the piston stop thave been shown, it will be readily apparent that this arrangement canbe designed with rubber springs or other elastic devices. Thearrangement can be designed also without the output selector 6 byconnecting the upper end of the spring 5 or elastic device directly tothe piston rod 3. Inthis case the arrangement would lack the possibilityof varying the maximum pressure. It can also be designed without thecounterbore in the piston 3 which would render the operation of the pumpless eicient.

While I have shown and described a particular embodiment ofthisinvention, further modifications and improvements will occurto'tho'se skilled in the art. 4I desire it to be understood, therefore,that this invenif tion is not limited to the form shown, and I intend inthe appended claim to cover all modications which do not depart from thespirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An improved reciprocating pump comprising:

a cylinder,

a piston having an Vaxial bore lreciprocable, inthe cylinder betweenpredetermined limits and in essentially tluid tight relationship withthe cylinder,

a piston ro'd extending through the bore in the piston in slidingengagement therewith and in essentially liuid tight relationshiptherewith,

piston stop means on one'end ofsaid piston rod,

elastic compression means coupling the piston and vpiston rod for'normally urging the piston against the piston stop means and fortransmitting a predetermined force from the piston rod to the piston,

the end of said cylinder toward which said elastic compression meansurges said piston including an inlet port and an outlet port, thecylinder wall being free of any other ports between said end of thecylinder and the reciprocating limit of the piston remote from said endof the'cylinder,

an input line coupled to said input port,

a check valve between the input line and the input port,

an output line coupled to said output'port,

a check valve between the output line and the output port,

drive means of sullicient power for reciprocating the piston rod evenwhen there is no flow from the cylinder to the output line, thecompression means maintaining the piston in engagement with the stopmeans during reciprocating of the piston rod except when the pressurebetween 'the piston and said end of the cylinder exceeds apredeterminedl'evel,

whereby when the pressure between the piston and Said end of saidcylinder exceeds said predetermined level said piston is slidable alongthe piston rod to maintain substantially'constant pressure in saidcylinder.

References Cited by the y)Examincr UNITED STATES PATENTS 1,369,915 3/21Church 103-.17 1,829,451 10/31 McNab 103-37 1,871,040 S/32 CarterV'103--3 8 1,919,040 Y 7/33 Rockwell 103-38 1,981,667 11/34 Rockwell103-38 2,756,683 7/'56 Newman 103-211 3,112,705 12/63 Chlebowski 103-37LAURENCE V. EFNER, Primary xamer.

